Process for melt spinning

ABSTRACT

FILAMENTS BY MELT-SPINNING THROUGH PLURALITY OF PACKS WITH VARIATION OF HEAT LOSSES FROM FREE FACES OF PACKS MINIMIZED BY SHIELDS IN CLOSE PROXIMITY WITH SUBSTANTIALLY IDENTICAL TEMPERATURES.

Aug. 14, 1973 CQATES 3,752,874

PROCESS FOR MELT SPINNING Filed July 26, 1971 United States Patent ()1ice 3,752,874 Patented Aug. 14, 1973 PROCESS FOR MELT SPINNING RonaldBell Coates, Harrogate, England, assignor to Imperial ChemicalIndustries, London, England Filed July 26, 1971, Ser. No. 165,985 Claimspriority, application Great Britain, Aug. 4, 1970, 37,582/ 70 Int. Cl.B28b 3/20; B29c 25/00 US. Cl. 264176 F 21 Claims ABSTRACT OF THEDISCLOSURE Filaments by melt-spinning through plurality of packs withvariation of heat losses from free faces of packs minimized by shieldsin close proximity with substantially identical temperatures.

The present invention relates to the melt-spinning of fibre-formingpolymers, more particularly to the minimizing of variability inperformance between the members of a set of spinnerets producing asingle type of filament.

According to the present invention we provide a process for themanufacture of filaments by the melt-spinning of a fibre-forming polymerthrough a plurality of spinning packs each having a spinneret with aface exposed to the ambient atmosphere, wherein variation between therates of loss of heat from the exposed faces of the various spinneretsis minimized by the close proximity to the exposed spinneret face of ashield of substantially the same size and shape as the exposed spinneretface, at least the faces of said shields directed towards said exposedspinneret faces being maintained at substantially constant andsubstantially identical temperatures.

According to our invention we also provide a spinneret with a faceexposed to ambient atmosphere and associated therewith in closeproximity a shield of substantially the same size and shape as thespinneret.

'Normally a spinneret for melt-spinning derives its heat indirectly froma heat transfer medium which is con-veniently a fluid but may also be ametallic block heated by, for example, electrical means. Since the heattransfer medium is normally kept at a constant temperature throughout abank of spinning units, it is preferable that the shield of ourinvention shares the same source of heat. Preferably the temperature ofthe shield should differ from that of the heat transfer medium by nomore than 50 C., and more desirably by no more than C.

The shield should be of such form that the threadline or threadlines donot contact it in passing. Thus, for example, a hole, or holes areprovided in the shield opposite the spinneret orifices. the edges ofsaid hole, or holes, being at least one sixteenth of an inch away fromthe nearest filament.

The shield may be fixed or it may be movable or removable to permitwiping of the spinneret face.

A shield may be in more than one part. For example in the case whereinthe pattern of spinneret holes constitues a straight line the shield maybe in two parts one each side of the straight line, the two parts of theshield delineating a narrow band free from shielding and in which thespinneret holes are situated.

The shield should preferably not be in contact with the spinneret face,since extent and intimacy of contact are not subject to accuratecontrol. We have found it advantageous to arrange for the shield at nopoint to be distant from the spinneret face by less than one thirtysecond of an inch. On the other hand, the shield should not be distantby more than one inch from the spinneret face. We have foundparticularly good results when the shield is substantially uniformlydistant from the spinneret face throughout its area and the distanceapart is one eighth of an inch.

The facility for temporarily moving or removing the shield from itsproximity with the spinneret face implies flexibility in, or the abilitytemporarily to disconnect, the means for conveying heat to or removingheat from the shield.

Since uniformity of heat loss from the spinnerets is aimed at, actualheat losses should be minimized, thus the face of the shield directedtowards the spinneret face should preferably be polished, for example itmay be chrome plated. Since controlling the temperature of the shield atthe desired level is facilitated by minimizing heat losses from it, itsface directed away from the spinneret face should also preferably bepolished. Whilst it is advantageous that the material of construction ofthe shield should be of high thermal conductivity so that heat is freelypassed between the face of the shield directed towards the spinneretface and the heat conveying means, the side of the shield directed awayfrom the spinneret face may be provided with a layer of low conductivitywith advantage. The material of high conductivity may, for example, becopper, aluminium or silver; the layer of low conductivity may forexample, be a layer of asbestos or a chamber which contains air or whichis evacuated.

'By the use of the process of our invention, variation in heat lossesfrom the exposed face of the various spinnerets can be reduced, therebyreducing the variation in temperature from one spinneret to another andthus producing fibre of more uniform properties, for example a moreuniform dye uptake. Moreover, by the use of our invention it ispossible, in view of the minimizing of heat losses, to ensure thedesired extrusion temperature with a lower temperature of the moltenpolymer within the pack, with consequent minimizing of thermaldegradation.

A specific embodiment of our invention will now be described withparticular reference to FIGS. 1 and 2 in which FIG. 1 shows a verticalsection through a spinning pack and shield and FIG. 2 shows a view frombelow the spinneret of FIG. 1.

Referring to FIGS. 1 and 2, a spinning pack 1 has spinneret 2 at itslower part. The spinning pack 1 is heated by a vapour jacket 3 and thepack 1 and vapour jacket 3 are insulated by a muff 4, an insulating lid5 and insulation 6. Below the spinneret 2 there is situated a spinneretshield 7 of copper 0.75 inch thick and distant from the lower, free faceof the spinneret 2 by A; inch. The shield 7 is insulated by insulation8. The shield 7 is in good metallic contact with wall of the vapourjacket 3. The lower face of the spinneret 2, which without the shield 7would be exposed to the ambient atmosphere, is circular and of diameter5 inches. The proportion of the face of the spinneret 2 which isshielded by the shield 7 is The spinneret 2 bears two rows of spinneretholes 9. Filaments extending downwards from the spinneret holes aredistant from the nearest point of the shield 7 by 0.25 inch.

What I claim is:

1. In a process for the manufacture of filaments by the melt-spinning ofa fibre-forming polymer through a plurality of spinning packs eachhaving a spinneret with a face exposed to the ambient atmosphere andheating the spinneret, the step of minimizing variation between therates of loss of heat from the exposed faces of the various spinneretsby disposing in close proximity to the exposed spinneret face a shieldof substantially the same size and shape as the exposed spinneret face,and maintaining at least the faces of said shields directed towards saidexposed spinneret faces at substantially constant and substantiallyidentical temperatures.

2. A process for the manufacture of filaments according to claim 1wherein the heating of the spinneret also heats said shield.

3. A process for the manufacture of filaments according to claim 2wherein the spinneret and shield are heated with a heat transfer fluid.

4. A process for the manufacture of filaments according to claim 1wherein the temperature of the shield differs from that of the heattransfer medium by no more than 50 C.

5. A process for the manufacture of filaments according to claim 1wherein the temperature of the shield differs from that of the heattransfer medium by no more than C.

6. A process for the manufacture of filaments according to claim 1wherein no part of the shield lies nearer than one-sixteenth of an inchaway from the nearest filament.

7. A process for the manufacture of filaments according to claim 1wherein the shield is not in contact with the spinneret face.

8. A process for the manufacture of filaments according to claim 1wherein the shield is at no point distant from the spinneret face byless than one-thirty-second of of an inch and the shield is not distantfrom the spinneret face by more than 1 inch.

9. A process according to claim 8 wherein the shield is uniformlydistant from the spinneret face throughout its area and the distanceapart is one-eighth of an inch.

10. A process for the manufacture of filaments according to claim 1wherein the side of the shield directed away from the spinneret face isprovided with a layer of low conductivity.

11. Apparatus for the manufacture of filaments by melt-spinningcomprising: a plurality of spinning packs each having a spinneret platewith a face exposed to ambient atmosphere; means for heating thespinneret packs; a shield for minimizing variations between the rates ofloss of heat from the exposed faces of the spinnerets, said shieldhaving a size and shape substantially the same as the exposed spinneretface and having faces directed toward said exposed faces, said shieldfaces being closely spaced to but not in contact with said exposedfaces; and means for maintaining at least said faces of said shield at asubstantially constant temperature which is substantially the same asthe temperature of said spinneret faces.

12. Apparatus as in claim 11 wherein the shield is at no point distantfrom the spinneret face by less than onethirty-second of an inch normore than one inch.

13. Apparatus as in claim 11 wherein the proportion of the face of thespinneret which is shielded by said shield is at least about 75% 14.Apparatus as in claim 11 wherein said shield includes a metal platedisposed parallel to said spinneret plate, said metal plate having atleast one aperture through which at least one filament passes from thespinneret plate, the wall of said aperture being spaced from the movingfilament.

15. Apparatus as in claim 14 wherein the means for heating the spinneretpacks includes a jacket for passing a heated fluid in heat transmissionrelationship with the packs, and wherein said shield is disposed in heattransmission relationship with said jacket.

16. Apparatus as in claim 11 wherein no part of the shield lies nearerthan one-sixteenth of an inch away from the nearest filament.

17. Apparatus as in claim 11 wherein said shield is movable so as topermit wiping of the spinneret face.

18. Apparatus as in claim 11 wherein the face of said shield directedtowards the spinneret face is polished.

19. Apparatus as in claim 11 wherein the face of said shield directedtowards the spinneret face is chrome plated.

20. Apparatus as in claim 11 wherein said shield is constructed of ametal selected from the group consisting of copper, aluminum and silver.

21. Apparatus as in claim 11 including a layer of low thermalconductivity on the side of the shield directed away from the spinneretface.

References Cited UNITED STATES PATENTS 3,129,272 4/1964 Ferrier et a1.264-176 F 3,466,357 9/1969 Schippers et al. 264-176 F 2,303,340 12/ 1942Dreyfus 264-176 F 2,318,679 5/1943 Dreyfus 264-176 F 2,437,685 3/1948Dreyfus 264-176 F 2,683,073 7/ 1954 Pierce 264-176 F 3,130,448 4/ 1964Tomlinson 264-176 F 3,282,668 11/1966 Mahru 264-176 F 3,437,725 4/ 1969Pierce 264-176 F 3,512,214 5/1970 Shiba et al 264-176 F 3,517,412 6/1970Swanson et al 425-72 FOREIGN PATENTS 929,306 6/ 1963 Great Britain264-176 F 723,067 12/1965 Canada 264-176 F 36/8,291 4/1961 Japan 264-176F 37/5,260 6/1962 Japan 264-176 F 41/17,929 10/1966 Japan 264-176 F JAYH. WOO, Primary Examiner US. Cl. X.R.

